Numerous insects are vectors for disease. Mosquitoes in the genus Anopheles are the principle vectors of malaria, a disease caused by protozoa in the genus Trypanosoma. Aedes aegypti is the main vector of the viruses that cause Yellow fever and Dengue. Other viruses, the causal agents of various types of encephalitis, are also carried by Aedes spp. mosquitoes. Wuchereria bancrofti and Brugia malayi, parasitic roundworms that cause filariasis, are usually spread by mosquitoes in the genera Culex, Mansonia, and Anopheles. 
Horse flies and deer flies may transmit the bacterial pathogens of tularemia (Pasteurella tularensis) and anthrax (Bacillus anthracia), as well as a parasitic roundworm (Loa loa) that causes loiasis in tropical Africa.
Eye gnats in the genus Hippelates can carry the spirochaete pathogen that causes yaws (Treponema pertenue), and may also spread conjunctivitis (pinkeye). Tsetse flies in the genus Glossina transmit the protozoan pathogens that cause African sleeping sickness (Trypanosoma gambiense and T. rhodesiense). Sand flies in the genus Phlebotomus are vectors of a bacterium (Bartonella bacilliformis) that causes Carrion's disease (oroyo fever) in South America. In parts of Asia and North Africa, they spread a viral agent that causes sand fly fever (pappataci fever) as well as protozoan pathogens (Leishmania spp.) that cause Leishmaniasis.